FR2846798A1 - Bipolar plate for fuel cells used in vehicle electrics, especially urban buses and trams, but also for fixed installations such as hospitals, has two metallic plates with silicone sealing joints between them - Google Patents

Abstract

The bi-polar plate has a framework comprising two metallic plates (20) having recesses at two levels making up two circulation channels for fuel (21S,21l), with an internal space for refrigerant liquid, and providing a peripheral space permitting the placing of a casing (11) for the distribution of refrigerant, and fuel. Two joints (4,5) and a spacer (16) completes the mounting.

Description

BIPOLAR PLATE WITH TWO METALLIC PLATES FOR CELL PILE

COMBUSTIBLE

DESCRIPTION

  Field of the Invention The invention relates to the field of fuel cells consisting of a stack of a large number of stages, each comprising two pole plates 10 through which the oxidant and the fuel are conveyed to a separating membrane placed

between the two pole plates.

  This type of fuel cell can find its application in electric vehicles which are currently the subject of numerous development studies, in particular urban surface public transport vehicles, such as buses, trams and other trolley buses. Many other applications are possible, in particular on fixed installations, such as stationary electricity production systems, such as those used in hospitals or other service buildings where the possibility of an interruption of electricity supply must be excluded. PRIOR ART AND PROBLEM POSED Many fuel cells consist of a succession of stages each comprising a basic element 30 consisting of two electrodes, including an anode and a cathode, to which an oxidant and a fuel are continuously supplied, and which remain separated by an ion exchange membrane acting as an electrolyte. The ion-exchange membrane may be formed from a solid polymer electrolyte and separates the anode compartment, where oxidation of the fuel, such as hydrogen, takes place from the cathode compartment, o the oxidant, such as oxygen in the air, is reduced. Two simultaneous reactions therefore occur at this level, the oxidation of the fuel at the anode 10 and the reduction of the oxidant at the cathode. These two reactions are accompanied by the establishment of a

  potential difference between the two electrodes.

  When the oxidant is oxygen, for example in the form of air, and the fuel is pure hydrogen gas, the ions H ′ and 0 combine and produce electricity in the form of this difference potential. The reaction can be detailed as follows at the anode

2H2 + 40H- - 4H20 + 4th_.

  The reaction at the cathode is explained by the following formula

02 + 2H20 + 4th - 40H-.

  Each stage of a fuel cell stack consists of a basic element therefore comprising the membrane, sandwiched between the two electrodes, this element itself being placed between two flanges, called "pole plates" . These

The latter have several functions.

  The first of these functions is to bring into contact with the assembly uniting the membrane and the 5 electrodes, on one side the fuel, for example hydrogen, and on the other side the oxidizer, for example air containing oxygen. To do this, a channel is provided on the entire face of the pole plates in contact with the membrane. Each channel 10 has an inlet through which the oxidant or fuel enters, for example in the dry or wet gaseous form, and an outlet through which the neutral gases, the water generated by the redox reaction are discharged into the air side. and the residual hydrogen moisture on its side. Of course, the two circuits must be perfectly sealed with respect to each other and each vis-à-vis the outside. The second function of the polar plates is to collect the electrons produced by the redox reaction. On the other hand, from French patent application FR-2 810 795, a bipolar plate for a fuel cell is known which is composed of two metal plates. The latter are parallel, kept at a distance from each other and constitute a skeleton around which a body is molded. Thus, a refrigerant circulation circuit is formed between the two plates, while the external surfaces of the body are molded so as to present channels of

  circulation of oxidizer and fuel.

  Summary of the Invention The main object of the invention is therefore a bipolar plate constituting the first pole plate of a base element of a fuel cell and the second plate of a second base element adjacent to the first basic element of the same fuel cell, comprising - a single body made up of two metal plates fixed to each other and thus delimiting between them a first space to allow circulation of coolant, and on each free surface of which is formed at least one fuel or oxidizer circulation channel; and - a frame placed at the periphery of the single body, - manifold holes being provided at the periphery of the metal plates constituting the single body and the frame, to constitute fuel and oxidizer collectors, supply channels located between the metal plates and connecting the holes of

  manifold to circulation channels.

  According to the invention, the two metal plates each have a relief defining at least one circulation channel and parts of contact between them, while delimiting a refrigerant circulation circuit. In the preferred embodiment of the invention, the metal plates are stamped before being assembled. This avoids any untimely, long and costly machining of the channels, especially in the case where

these are very complicated.

  Preferably, the parts in contact with the two metal plates are brazed to each other,

two by two.

  In the preferred embodiment of the invention, the frame is metallic, and brazed on the internal face

  of each of the two metal plates.

  Preferably, the bottom of the channels has a

maximum sinking of the plates.

  In order to ensure sealing between two adjacent bipolar plates, each of them comprises silicone seals implanted the metal plates 15 at the level of the low penetration part, around the fuel and oxidizer collectors and at the periphery of the membrane of a

membrane / electrodes assembly.

  In the latter case, it is advantageous to provide that, in each bipolar plate, a range of slight recess is used at the periphery to provide access to radial collectors formed in the frame, to position the joints and present a support or a

retractor / seals system.

  Several constructions of the fuel and oxidant circulation channels are planned. Indeed, realizations in zigzag, in grid, in helices and in square or even rectilinear spirals can be envisaged. List of figures The invention and its various characteristics

  techniques will be better understood on reading the following description, which is accompanied by six

  Figures representing respectively: - Figure 1, in partial section, the bipolar plate according to the invention; - Figure 2, in partial top view, a detail 10 of the fuel circuit in an embodiment of the bipolar plate according to the invention; - Figure 3, in top view cut away, a second embodiment of the bipolar plate according to the invention; - Figure 4, in cutaway view, part of the same second embodiment of the bipolar plate according to the invention; - Figure 5, in cutaway view, a detail of a third embodiment of the bipolar plate 20 according to the invention; and - Figure 6, in cutaway view, a detail of a fourth embodiment of the plate

bipolar according to the invention.

  Description of preferential achievements of

  The invention Referring to FIG. 1, the bipolar plate according to the invention is shown jointly with two membrane / electrode assemblies 1, which it maintains while separating them. Each membrane / electrode element 1 therefore has a membrane 3 sandwiched between two electrodes 2. Each element is positioned on the bipolar plate 10, the peripheral part of each membrane 3, protruding by 5 relative to the two electrodes 2 and being supported on A

membrane seal 4.

  The bipolar plate 10 mainly comprises two metal plates 20 fixed to one another, which extend over the entire surface of the bipolar plate. 10 The bipolar plate 10 is completed with a frame 11

  consisting of a spacer 13 closed, on its two sides, by two annular plates 12. This frame 11 is placed between the two plates 20 which deviate at their periphery by an interval equal to the thickness of the frame 15 11.

  The bipolar plate is crossed, at its

  periphery, by several vertical collectors which cross the entire stack of the fuel cell.

  Thus, the two metal plates 20 are pierced by 20 collector holes 28 as the annular plates 12 are provided with collector holes 15. At this level, the bipolar plate is completed with a ring called spacer 16 which has the purpose of keep apart adjacent bipolar plates 10. An annular seal 5 placed around the manifold holes completes the assembly. Note that the manifold holes 28 at the periphery of each metal plate 20 have a flange 29 thus allowing the annular seal 5 to be positioned, the spacer 16 itself also having a

  shape corresponding to that of the annular seal 5.

  The seals 4 and 5 are preferably made of silicone. As can be seen, each spacer 13 has a distribution space 16 connecting the manifold holes 5 and 28 to a supply hole 14 intended for the circulation of fuels, that is to say on the one hand the oxidizer, and, on the other hand

fuel.

  The metal plates 20 have a relief shape made up of several bosses and

  dents. In fact, they have, in particular, a maximum depression at the level of the contact parts 22 which allow the two metal plates 20 to be in contact with one another. This therefore makes it possible to fix them effectively by brazing.

  Each metal plate 20 also has a

  slight sinking towards its periphery, allowing space necessary to accommodate the frame 11 there.

  In this regard, each metal plate 20 has at least one supply hole 23 placed opposite a

  feed hole 14 of an annular plate 23.

  Thus, it can be seen that the fuel and oxidizer supplied by the manifolds can flow from the manifold holes 15 and 28, then through the supply space 17 and the supply holes 14 and 23.

  Thus they reach circulation channels 21F and 21I shaped, inter alia, by virtue of the maximum insertion at the level of the contact parts 22, outside the assembly formed by the two metal plates 30 which are fixed to the one to the other.

  It is emphasized that the two plates 20 are stamped so as to present symmetrical patterns. Thus, when they are joined against each other, the parts in contact 22, at the level of the deepest depression, can be brazed against each other.

  the other. This design makes it possible to obtain three volumes or circuits isolated from each other, that is to say two fuel circulation circuits and one circulation of the refrigerating fluid.

  At another more external level, each metal plate 20 has another slight depression 26, at the level of the annular seal 4, thus allowing the latter to be positioned relative to the assembly of the bipolar plate 10. At the locations o the metal plates 20 do not have any depression, that is to say where they are spaced apart the most from one another, they define a space for circulation of the

refrigerant 28.

  The refrigerant is conveyed in spaces or

  refrigerant circulation channels 28 in a similar manner to that shown in this figure 1.

  In view of the fact that the contact parts 22 of the two metal plates 20 are not continuous over the entire surface or the periphery of the bipolar plate 10, the refrigerant can have access to a peripheral space 29. It is conveyed there by a supply space and collector holes not shown but similar to those shown in this FIG. 1. If, in addition, at the coolant collector, each metal plate 20 does not have a recess at the level of the supply 14 of the spacer 11 and does not itself have supply holes 23, the refrigerant can therefore pass through the supply hole 14 and slip between the two metal plates 20. In fact, each plate 20 has two levels of depression, a level of total depression at the level of the contact parts 22 and a level of slight depression on the periphery, at the level of the annular plates 10 of the frame 11. The alternation of the depths ements of the metal plates 20 allows both the circulation of the coolant and that of the fuels. A concrete embodiment provides that the maximum insertion of a plate is about 1.4 mm and that the

  slight indentation of the order of 0.5 mm.

  It will be noted that the annular seal 4 serves as a support for the membrane 3 of the membrane / electrodes element 1. In fact, its thickness is slightly greater than the depth of the light

  sinking at the periphery of each metal plate 20. The difference in height corresponds to a little more than the thickness of each electrode 2, so as to allow slight sinking of the annular seal 4.

  Similarly, the spacer 16 and the annular seals 5 which it positions are both centered also thanks to the slight depression at the extreme periphery 27 of each metal plate 20, together with the flange 29, formed around each hole of manifold 28. il FIG. 2 makes it possible to understand part of the hydraulic circuit, and in particular at the junction between the circulation channels 21S and 21I with the supply spaces 16 in the frame 11. 5 The dashed lines represent the internal forms of the frame there which, in fact, are presented in an annular manner, that is to say that it completely surrounds a whole stage of the stack of a fuel cell. The supply holes 14 and 23 have been represented by several orifices, these being a possible embodiment. Vertical to the latter is the start of the circulation channels 31S and 31I. Here they have a spiral shape,

  but this is only a first embodiment.

  Figure 3 shows another embodiment of the bipolar plate, the stack of the fuel cell being square. Thus, each frame there of each floor is also square in shape. In this embodiment, the spacer 13 has been shown cut and distinct from a frame frame 31 which supports the four spacers 13. However, this is only an embodiment dictated by ease of manufacture in several pieces . The inputs EH and EO and outputs SH and SO of the two fuels, for example oxygen and hydrogen, are placed opposite one another, so that each fuel can pass right through share all the circulation channels 41S and 41I. The shape of the reliefs is shown in detail in FIG. 4. It is a multitude of small squares 42 forming a grid in the form known as "in plate of

chocolate ".

  Figure 5 shows another form of relief, called "groove" or "straight". In this case, the fluid circulates on parallel channels 51S and 51I. Figure 6 shows an embodiment of the

channels 61S and 61I in zigzag.

  It is easy to understand that the production of metal plates 20 by stamping makes it possible to envisage a multitude of different reliefs for

  create circulation channels.

  It is noted that the assembly of a stack of fuel cells, that is to say all the two plates of a stack can be brazed in a single operation, which greatly facilitates the manufacture of the assembly.

and reduces its production cost.

Claims (10)

REVENDI CATIONS   1. Bipolar plate (10) constituting the first pole plate of a base element (1) of a fuel cell and the second pole plate of a second base element (1) adjacent to the first base element of the same fuel cell, comprising: - a single body consisting of two metal plates (20) fixed to each other and 10 comprising a first space (28) allowing circulation of the refrigerant, and on each free surface of which is formed at least one circulation channel (21S, 21I, 31S, 31I, 41S, 41I, 51S, 51I, 61S and 611) of fuel or oxidizer; and - a frame (11, 31) placed at the periphery of the single body, manifold holes (15, 28) being provided at the periphery of the metal plates (20) and of the frame (11) to constitute coolant collectors , supply spaces (16), located between the metal plates (20) and connecting the manifold holes (15, 28) to the circulation channels (21S, 21I), via 25 supply holes ( 14, 23), characterized in that the two plates   metallic (20) have a relief defining the circulation channels (21S, 21I) and contact parts (22) therebetween, while delimiting between them a refrigerant circulation circuit (28).   2. Bipolar plate according to claim 1, characterized in that the metal plates (20)   are stamped before being assembled.   3. Bipolar plate according to claim 1 or 2, 5 characterized in that the metal plates (20) are assembled by brazing to their contact parts (22). 4. Bipolar plate according to claim 2, characterized in that the bottom of the circulation channels (21S, 21I, 31S, 31I, 41S, 41I, 51S, 51I, 61S, 61I) is obtained by maximum depression of each plate metal (20), and in that each of the metal plates (20) has a slight recess (26) at the periphery to provide access to the supply spaces to the circulation channels 15   (17) placed inside the frame (11), position the seals (4, 5) and present a support for the assembly consisting of a spacer (16) and the annular seal (5).   5. Bipolar plate according to claim 1, 20 characterized in that it comprises a silicone seal (4) placed on the surface of the metal plates (20) at the level of the part of low penetration (26), around the membrane (3) a membrane / electrode assembly (1), in order to ensure   the seal between two bipolar plates (10).   6. Bipolar plate according to claim 1, characterized in that the shape of each bipolar plate (10) being square, the circulation channels   of each plate has a square spiral shape.   7. bipolar plate according to claim 1, characterized in that the assembly of the bipolar plate being round, the circulation channels (31S, 31I) have a helical shape.   8. Bipolar plate according to claim 1, characterized in that the circulation channels (41S, 41I) have a grid shape. 9. Bipolar plate according to claim 1, characterized in that the circulation channels (51S, 51I) have a rectilinear shape.   10. Bipolar plate according to claim 1, 10 characterized in that the circulation channels (61S, 61I) have a zigzag shape.